Electronic devices (e.g. PCs, cellphones, PDAs), lighting and display devices (e.g. LED, EL) and the like have recently made a significant improvement in performance. This improvement is attributed to a significant improvement in the performance of arithmetic elements and light-emitting elements. The improvement in the performance of arithmetic elements and light-emitting elements has been accompanied by a significant increase in the amount of heat generation, which may cause malfunctions in electronic devices and lighting and display devices or cause damage to electronic components. This poses the important challenge of how to dissipate heat from such elements. Further, from the standpoint of preventing burn injuries during the use of electronic devices such as PCs or cellphones, it is important for these devices to avoid conduction of heat to the outside in portions that come into contact with the human body, while conducting heat to portions that do not come into contact with the human body.
Known measures to dissipate heat from such electronic components as described above include techniques using a thermally conductive resin molded product as disclosed in Patent Literature 1, and techniques using a heat-dissipating sheet as disclosed in Patent Literatures 2 to 4. A problem associated with the use of molded products is that additional work is required to modify the mold and the like for each component. Moreover, since not only electric/electronic components but also other many heat-generating elements and heat-dissipating elements have non-smooth surfaces, heat dissipation components in the form of heat-dissipating sheets cannot be put in close contact with these heat-generating elements and heat-dissipating elements, and therefore the contact area with the heat-generating element or heat-dissipating element is reduced. On such printed circuit boards as described above, electronic components of various sizes from small to large are used, and therefore the heat dissipation components such as heat-dissipating sheets cannot conform to the fine irregularities. This reduction in contact area problematically causes a reduction in the efficiency of heat transfer from the heat-generating element to the heat-dissipating element, which does not allow the heat dissipation components to sufficiently exhibit their heat dissipation properties.
Moreover, Patent Literature 5discloses a technique of embedding in a heat-dissipating resin electronic components on the front and back surfaces of a printed circuit board to reduce differences in heat dissipation and provide efficient heat dissipation. However, since the disclosed resin is a conductive rubber, an extra step of further providing an insulating layer to the front and back surfaces of the printed circuit board is required after application of the heat-dissipating resin. In addition, since the resin applied to the front and back surfaces of the printed circuit board transfers heat to all directions, the direction for heat dissipation cannot be controlled. The heat is therefore conducted to portions that come into contact with the human body during the use of the electronic device, which leads to the risk of burn injuries during the use.
Furthermore, Patent Literature 6 describes a heat dissipation technique for allowing heat to escape to a certain inside area to prevent thermal conduction to the outside. This technique includes connecting a base substrate to a heat-generating substrate on which electronic components are placed, so as to transfer heat generated by the electronic components to the base substrate. However, since this technique requires multiple substrates, it is difficult to make a space in the electronic devices desired to be miniaturized and reduced in thickness, and the design of these devices is also required to be greatly changed.